It is our hypothesis that typical and atypical antipsychotic drugs exert their actions via distinct molecular changes in cell populations that impinge upon and participate in striatal signaling. By identifying what these changes are, we will identify common signaling pathways that are linked to the therapeutic effects of antipsychotic drugs. Project 1 of this Conte center application will focus on striatal cell-specific changes in mRNA translation induced by antipsychotic drug administration. For this purpose we will use our newly developed Translating Ribosome Affinity Purification (TRAP) methodology. In Aim 1 we will use TRAP to identify mRNA translational alterations in the major populations of striatal dopaminoceptive and dopaminergic cells: striatonigral medium spiny neurons (MSNs);striatopallidal MSNs;cholinergic intemeurons;and dopaminergic neurons of the substantia nigra pars compacta and ventral tegmental area. Our preliminary TRAP studies have revealed that sphingosine 1-phosphate (SIP), a ligand for the striatopallidal MSN-enriched S1P receptor Gpr6, can alter both calcium levels and DARPP-32 phosphorylation levels in MSNs. Thus, S1P and Gpr6 may be capable of modulating striatopallidal cell physiology and their response to antipsychotic drugs. In Aim 2, we will characterize the role of 81P and Gpr6 signaling in the response of striatal MSNs to antipsychotic drug treatment using a combination of genetic, pharmacological, and biochemical approaches.